Fabrication of 3D Macroscopic Graphene Oxide Composites Supported by Montmorillonite for Efficient U(VI) Wastewater Purification

In this work, montmorillonite (MMT) was intercalated into a sheet of GO and then cross-linked by agar, realizing the 3D macroscopic composites of agar-MMT-GO. Agar-MMT-GO composites were characterized by SEM, TEM, FTIR, TGA, and XPS techniques. Fabricated agar-MMT-GO composites were tough and lightweight materials with a multichannel structure. The heat stability of agar-MMT-GO composites were enhanced relative to GO, as demonstrated by TGA results. FTIR analysis testified to no chemical bond between GO and MMT component, suggesting that agar scaffold mainly caused the formation of agar-MMT-GO composites. Agar-MMT-GO composites exhibited a good performance in U­(VI) sorption (<i>Q</i>_max of 147 mg/g at pH 4.5) and in recycling tests. The rate-limiting sorption step was the diffusion of U­(VI) from liquid solution to the surface sites of agar-MMT-GO composites. XPS analysis demonstrated that U­(VI) sorption on agar-MMT-GO was mainly attributed to cation exchange and inner-sphere complexation in low and high pH regions, respectively. Briefly, our work here provides new insights in designing GO composites with a solid skeleton to promote its large-scale application in wastewater remediation

Microscopic and Spectroscopic Insights into Uranium Phosphate Mineral Precipitated by <i>Bacillus Mucilaginosus</i>

In this paper, we used spectroscopic and microscopic techniques to investigate the interaction mechanism between uranium and <i>Bacillus mucilaginosus</i>. According to scanning electron microscope couple with energy dispersive X-ray detector analysis, the lamellar uranium phosphate precipitation was only observed on the living <i>B. mucilaginosus</i> and the resting <i>B. mucilaginosus</i>. The Fourier transform infrared spectroscopy spectrum also indicated the important role of phosphate groups in forming U­(VI)-phosphates precipitation. The X-ray diffraction analysis identified the phase of U­(VI)-phosphate precipitation as H₃OUO₂PO₄·3H₂O. Batch experiment showed that biominerilization amount could be up to 195.84 mg/g when exposing living <i>B. mucilaginosus</i> to U­(VI) aqueous solution at pH 5.0 for 1 h. The precipitate was further evidenced by extended X-ray absorption fine structure spectra based on the presence of U–P shell, which demonstrated that hydrogen uranyl phosphate became the main products on the living <i>B. mucilaginosus</i> with prolonged reacting time. After ashing and hydrothermal process, the precipitated U­(VI) on <i>B. mucilaginosus</i> could be converted into UO₂ and K­(UO₂)­(PO₄)·3H₂O. Our findings have significant implications in elucidating the potential role of bacteria in the migration of uranium in geological environment